Method for producing a hollow fiber membrane module or a capillary membrane module

ABSTRACT

The invention relates to a method for producing a hollow fiber membrane module or a capillary membrane module as well as a device having such a module. In the method, hollow fibers or capillaries are placed, in an unsintered state, in a mold structured for receiving the hollow fibers or capillaries and are sintered once inside the mold. Subsequently or simultaneously, the fibers are potted in the mold. The method permits producing hollow fiber membrane modules or capillary membrane modules in a simple manner with little risk of breakage.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention relates to a method for producing a hollowfiber membrane module or a capillary membrane module in which the hollowfibers or capillaries made of a ceramic or a material with a ceramiccontent are introduced into a mold structured for receiving the hollowfibers or capillaries and are potted in the mold with a pottingcompound. In addition, the present invention relates to a device havinga hollow fiber membrane module or a capillary membrane module producedaccording to the present method.

[0003] In the present invention, hollow fibers refers to pipe-shapedbodies with an external diameter in the range from approximately >10 μmto 0.5 mm, capillaries refers to bodies with an external diameterbetween 0.5 and 3 mm.

[0004] The present method and device are primarily employed infiltration and separation technology. In these technologies, among otherthings, inorganic membranes in the form of modules are utilized asseparation tools for the filtration of liquids as well as the separationof gases. The hollow fiber membrane module or capillary membrane moduleproduced with the present method can be utilized for separation of,respectively purification of, gases and vapors, in particular inhigh-temperature applications, as well as for the filtration of liquidsin micro-filtration, ultra-filtration and nano-filtration and as amembrane reactor.

[0005] 2. Prior Art

[0006] EP 0 941 759 A1 discloses a method for producing a hollow fibermembrane module in which the sintered hollow fibers are introduced intoa mold and are potted in this mold with a potting compound. Aceramic-containing compound is used as the potting compound, which isthen hardened respectively solidified in a suited thermal step. The moldfor receiving the hollow fibers is designed as a perforated plate, whichthen is fitted with the fibers potted inside it into a housing.

[0007] Production of a hollow fiber membrane module according to themethod of this printed publication is, however, difficult as thesintered hollow fibers have a great propensity to break as ischaracteristic of ceramics. It is not easy to handle such type sinteredhollow fibers so that insertion into the openings of the mold designedas a perforated plate is difficult and can lead to the hollow fibersbreaking.

[0008] EP 0 938 921 A1 discloses another method for producing a hollowfiber membrane module. In this method, a bundle of sintered hollowfibers is placed in a cylindrical mold and is potted in this mold whilethe potting compound is impinged with ultrasound.

[0009] However, in this method too the hollow fibers can break veryeasily.

[0010] The object of the present invention is to provide a method forproducing a hollow fiber membrane module or a capillary membrane moduleas well as a device having such a module, which is easy to produce andwith less risk of the hollow fibers or capillaries breaking.

SUMMARY OF THE INVENTION

[0011] The object is solved with the method and the device according toclaims 1 respectively 14. Advantageous embodiments of the method and thedevice are the subject matter of the subclaims.

[0012] In the present method for producing a hollow fiber membranemodule or capillary membrane module, hollow fibers or capillaries madeof ceramic or a material with a ceramic content in an unsintered state,i.e. as green fibers, are placed in a mold structured for the receptionof hollow fibers or capillaries. The hollow fibers or capillaries arenot sintered until once inside this mold in a thermal process step. Thehollow fibers or capillaries are potted, either before or aftersintering, with a potting compound, which connects them with the mold.This casting process is familiar to someone skilled in the art under theterm potting, the casting compound is called the potting compound. Thepotting compound is then hardened respectively solidified in such amanner that a hollow fiber membrane module respectively a capillarymembrane module is created which can be placed in a housing and utilizedin technical systems.

[0013] Solidification of the potting compound may occur, for example bymeans of a thermal process step. If a ceramic material is employed asthe potting compound sintering of the hollow fibers respectively thecapillaries and hardening can, therefore, occur in the same thermalstep. This technique is referred to as cofiring.

[0014] In the present method, the hollow fibers respectively thecapillaries are not inserted into respectively not placed in astructured mold in a sintered state but in a green state. This mold isthen part of the hollow fiber membrane module respectively of thecapillary membrane module and is shaped in such a manner that the hollowfibers respectively capillaries can be received in it. The mold can, forexample, be made of a porous ceramic or other inorganic materials, suchas for example metal or glass. Exemplary versions of preferredembodiments are grooved or corrugated, plate-like bodies or star-shapedbodies which, due to their geometry, have recesses to receive the fibersor capillaries. Placing the fibers in the mold can occur manually ormechanically. After being placed in the mold, the green fibers aresintered and potted.

[0015] There are various possible available methods for potting, such asfor example spinning, casting or tampon pressure. After the pottingcompound, preferably a ceramic or a polymer, has hardened, the hollowfiber ends respectively the capillary ends are cut off in such a mannerthat the lumina of the fibers are open. Cutting off the fiber ends canoccur by means of a suited severing method, for example using a diamondwire saw, by means of water jet blasting technology or by means of lasercutting technology.

[0016] With the proposed method, production of hollow fiber membranemodules or capillary membrane modules can be significantly simplified.Handling of the green fibers and placing them in a mold are renderedsignificantly easier and lead to far less breakage than when placingsintered fibers in a mold designed, for example, as a perforated platerespectively inserting a bundle of sintered fibers into a cylindricalbody. It surprisingly turned out that the ceramic hollow fibersrespectively capillaries do not connect during sintering but ratherremain separate. It is this surprising teaching of the inventors thatmakes producing a hollow membrane module or a capillary membrane modulewith the present method possible.

[0017] With this method fiber breakage and other defects can beprevented during production of the module. The fibers can, for example,be placed in bundles into the structured mold. During the subsequentdrying and sintering process, distortion respectively fraying of thefibers is prevented due to the external molding by the mold.

[0018] In addition to this, using a ceramic potting compound obviatesutilizing two separate thermal treatment steps. But rather sintering thehollow fibers respectively the capillaries and solidifying respectivelysintering the ceramic potting compound can occur in the same thermaltreatment step. In this case, the thermal expansion coefficients of thematerials for the hollow fibers respectively for the capillaries and thepotting compound must be matched in order to prevent the development ofexcessive mechanical tension.

[0019] The hollow fibers or capillaries can be provided in a prior artmanner as green fibers respectively in a green state. They can beobtained by spinning respectively by extrusion of inorganic or metalorganic compounds, such as preliminary polymer stages or inorganicbinder-containing suspensions of aqueous solutions of salts or of powderfilled sol/gels. Hollow fibers or capillaries produced in this mannerare flexible and easy to handle in a green state. In a sinteredrespectively pyrolyzed state, the hollow fibers or capillaries, such asemployed in the present method can be composed of oxidic substances suchas ZrO₂, TiO₂, α-Al₂O₃, γ-Al₂O₃, 3Al₂O₃*2SiO₂ (mullite), MgAl₂O₄(spinel), SiO₂, of perowskites, hydroxylapatite, zeolites, nonoxidicsubstances such as SiBNC, Sic, BN, Si₃N₄, C, as well as of metal such ascopper, titanium, iron, special steels or transition metal alloys. Thislist is, of course, incomplete. Someone skilled in the art is familiarwith suited materials for producing ceramic hollow fibers orcapillaries.

[0020] The material of the potting compound can be composed of the samematerial as the hollow fibers respectively the capillaries or of anothersuited inorganic or organic material. The expansion coefficients ofhollow fibers or capillaries and the potting compound should match.Preferably, the difference in expansion coefficient should be notgreater than 5×10⁻⁶K⁻¹. A higher thermal expansion coefficient of thefiber material can be tolerated more readily than the reverse.

[0021] The expansion coefficient of prior art materials for the pottingcompound respectively for the material for the hollow fibersrespectively for the capillaries are 8×10⁻⁶K⁻¹ for Al₂O₃, 10×10⁻⁶K⁻¹ forZrO₂(Y₂O₃ stabilized), 0.5×10⁻⁶K⁻¹ for SiO₂, 8−10×10⁻⁶K⁻¹ for TiO₂,4.5×10⁻⁶K⁻¹ for SiC. From these examples it is evident that there arenumerous materials that meet the above condition of a minor differencein thermal expansion coefficients.

[0022] In addition to a thermal process step, for example drying,solidification of the potting compound to the corresponding green statecan occur by changing the surface charge of the ceramic powder particlesof this potting compound. Such an change in the surface charge canoccur, for example, by means of enzymatic release of protons or hydroxylions.

[0023] For the intended use of the module produced according to theinvented method as a technical process device in a system for liquidfiltration or gas separation, the mold with the hollow fibersrespectively the capillaries potted in it are placed in a suitedhousing. The geometry of the mold containing the hollow fibersrespectively the capillaries and the housing are matched in such amanner that a so-called feed space for feeding the to-be-filtered mediumand a so-called permeate space for the filtrate are formed, which areseparated from each other in a gas tight manner by seals disposed in thehousing outside the membrane area respectively filter area, which isformed in a prior art manner by the side walls of the hollow fibersrespectively of the capillaries. The housing may be executed as a tightceramic or as a metal cartridge system.

[0024] In an alternative preferred embodiment, the green fibers, moldand a ceramic housing can be potted in a single step with a suitedpotting compound of ceramic and sintered together (cofiring). In thismethod of production, the relationship between size of the mold and thelength of the green fibers must be matched in such a manner thatshrinking of the fibers during subsequent sintering is taken intoaccount.

[0025] In addition to this, a module element produced in this manner canbe provided with further ceramic coatings, such as for example ofα-Al₂O₃, γ-Al₂O₃, MgAl₂O₄, TiO₂, ZrO₂, etc. with metal or metal alloycoatings, such as for example of transition metals from the groups 4-6,10, 11, in particular of alloys containing these transition metals, lavephases, metallic glasses or polymers such as for example polyimide. Thisadditional coating permits obtaining gas separation membranes and/orincreasing potting density.

[0026] A hollow fiber membrane module or capillary membrane moduleproduced with the present method respectively with the proposed devicewith such a type module can be used in many technical fields ofapplication. Examples are drying or moisturizing air (air conditioning),catalysis, cleaning hot gases, separation of gases, pervaporation, vaporpermeation, heterogeneous catalysis, use in membrane reactors, in heatexchangers, in contactors, in fuel cells, as prefilters forpurification, filtration of aggressive media such as hot acidic mediaand lyes or solvents, filtration of abrasive, toxic, microbiologicallyor otherwise contaminated liquids and the reprocessing of emulsions.

[0027] In the preceding description it was already made apparent thatvarious fiber/potting compound material combinations can be employed.Therefore, both oxidic and nonoxidic respectively metallic materials canbe used as the hollow fiber material respectively as the capillarymaterial and as the potting material. Hollow fibers respectivelycapillaries (hereinafter for the sake of simplicity only referred to asfibers) and the potting may be composed of the same materials or ofdifferent materials. The porosity of the potting material must be lessthan the porosity of the fibers. In the case of a combination of aceramic material for the fibers and a polymer for the potting, oxidicand nonoxidic respectively metallic materials can be used as the fibermaterial. In this case, polymers or organic materials, such as forexample epoxy resins (filled and not filled systems) or silicones can beemployed as potting materials. Here too, the porosity of the pottingmaterials must be less than the porosity of the fibers.

[0028] Preferably, the receiving mold also has the same or a similarthermal expansion coefficient as the fibers and the potting material. Inthis manner, tensions are prevented during production of the module andin its subsequent use at high temperatures.

[0029] The proposed device comprises a module produced according to thepresent method in a housing. The mold with the fibers and the housingare adapted geometrically in such a manner that a feed space and apermeate space are formed which are separated gas tight from each otherby seals or a sealing material between the mold and the housing but notwithin the membrane area. The housing has openings for the lumen inletand lumen outlet of the fibers and for the exterior inlet and exterioroutlet to respectively from the interior of the mold, which arepreferably designed as connections. In the same manner the mold formsopenings which permit feeding respectively removing gas or liquid viathe corresponding exterior openings of the housing to the exterior wallsof the fibers.

[0030] The housing with the fitted mold is preferably designed as acartridge system, with the mold and the cartridge being sealed in astuffing box-like manner between the lumen side and the exterior side ofthe fibers. The cartridge serves to adapt the device to the overallsystem. The interior of the receiving mold is accessible via thedescribed openings in the periphery of the mold. The housing ispreferably made of a metallic material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The method and the device are briefly described in the followingusing preferred embodiments with reference to the accompanying drawingswithout the intentions of limiting the scope or spirit of the inventiveidea.

[0032]FIG. 1 shows a first example of a mold with hollow fibers placedin it;

[0033]FIG. 2 shows a second example of a mold with potted hollow fibers;

[0034]FIG. 3 shows a third example of a mold with potted hollow fibers;

[0035]FIG. 4 shows an example of a preferred embodiment of the presentdevice as a cartridge system.

WAYS TO CARRY OUT THE INVENTION

[0036] FIGS. 1-3 show different examples of preferred embodiments of amold 1, as is utilized in the present method. In the example of FIG. 1,mold 1 is executed as a grooved plate made of ceramic or metal. Hollowfibers 3 in a green state are placed, preferably in bundles, into thegrooves 2 of the mold, as the figure shows. Following or simultaneouslywith the subsequent potting step, these fibers 3 are connected with mold1.

[0037] The mold (1) of FIG. 2 is designed star-shaped and preferablymade of a porous ceramic or porous metal. The hollow fibers 3 in a greenstate are placed in the recesses 4 formed by the star shape, sinteredand simultaneously or subsequently potted.

[0038]FIG. 3 shows a third example, in which mold 1 is formed by twoplates provided with hole openings 5. The green fibers are placed inthese openings 5 and then sintered and potted. In this manner a modulein the form of a multi-channel is formed, as FIG. 3 shows.

[0039] In all three examples, after the potting step fibers 3 are cutoff where their ends protrude from mold 1 in order to expose the fiberlumen.

[0040] Finally FIG. 4 shows an example of a preferred embodiment of thepresent device in the form of a cartridge system for insertion in asystem for filtering liquids or for gas separation. The capillarymembrane module or hollow fiber membrane module produced with thepresent method comprises in this example a cylindrical mold body 1 madeof glass or ceramic. In this mold 1, the ceramic hollow fibers orcapillaries 3 are potted at their ends. The potting compound bears thenumber 6. The material of mold 1 ideally has the same or a similarexpansion coefficient as the ceramic hollow fibers respectivelycapillaries 3 so that no thermal tension develops.

[0041] Mold 1 bears in its periphery in the region of its front end andrear end in at least one access opening 7 respectively via which theliquids reach the interior of the mold and in this manner the outersides of the ceramic hollow fibers or capillaries 3 respectively can beremoved from the interior of mold 1. A cartridge 10 which is preferablymade of metal or a high-temperature stable plastic bearing all theconnections for the lumen inlet and lumen outlet as well as the exteriorinlet and exterior outlet is pushed over this mold 1. The connectionopenings for the exterior inlet and exterior outlet 8 are locatedexactly over the access openings 7 of the mold.

[0042] The connections may be executed as threads or as welded hexagonnipples. The lumen connections 9 are attached to the housing 10 at thefront and provide access to the lumen of the hollow fibers respectivelycapillaries 3. These connections are also preferably designed as threadsor welded hexagon nipples. The diameter of mold 1 is adapted to theinner diameter of cartridge 10 in such a manner that there is onlyminimal play between the two. Preferably the two are connected in a formfitting manner. Seals 11, preferably square washers or O-ring seals, areprovided between mold 1 and the inner walls of cartridge 10, on the onehand, in order to seal between the lumen inlet and lumen outlet as wellas the exterior inlet and exterior outlet. The washers permit, on theother hand ensuring sealing between the exterior inlet and exterioroutlet. Washers 11 may, for example, be made ofhigh-temperature-tolerant polymers which are tolerant of hightemperatures and preferably also tolerant of chemicals, such as forexample polyimides, PTFE, Viton®, Kalrez®, silicon or of graphite ormetals.

[0043] In addition to washers, the entire intermediate space between themold body 1 and the cartridge 10 may also be filled with sealingmaterial—with the exception of the inlet and outlet openings 7, 8 forthe interior of the mold body 1—in such a manner that there is onlyminimum dead space.

[0044] Generating pressure force on the washers 11 can, for example,occur via swivel nuts, tie rods, or screws, with the thermal motionbeing offset via spring systems. The figure shows the use of a pressplate 12 by means of which a pluglike designed body 13 is pressed on theouter washers 11 between mold body 1 and cartridge 10. The two pressplates 12 are held together by threaded rods 14 with nuts.

[0045] A cartridge system as shown in FIG. 4 has the advantage that nothermal tension occurs in the capillaries or hollow fibers 3 from thereceiving mold 1, and it simultaneously permits simple adaptation of themodule to an entire system, for example a production system, via pipeconnections.

[0046] Three examples of variants of preferred embodiments of the methodfor producing a hollow fiber membrane module are given in the following.

[0047] In the first example, α-Al₂O₃ green fibers are utilized, whichwere produced according to the lycocell method of DE 44 26 966 A1. Thefibers are placed in a green state in bundles on a corrugated mold madeof porous Al₂O₃ ceramic, as for example shown in FIG. 1. The greenfibers are sintered in this mold at 1450° C. After the sintering step,the ends of the fibers are potted (static potting) with a two-componentepoxy-based adhesive compound (Biresin, hardener HM, SIKA Chemie) andthe potting compound is hardened in air for 24 hours. Following this,the hollow fibers are cut together with the mold in such a manner thatthe lumina of the fibers are open. A plurality of such molds with hollowfibers are transferred into a housing, with plastic seals separatingfeed and permeate spaces gas-tight.

[0048] In a second method, ZrO₂ green fibers that were also producedaccording to the lycocell method are utilized. The fibers are placed ina green state in bundles in a star-shaped mold made of Al₂O₃ceramic insuch a manner that the green fibers protrude beyond the boundary of themold. The degree of protrusion of the green fibers is selected tocompensate for the degree of shrinking during sintering (cf. FIG. 2).The inserted green fibers are sintered in the mold at 1200° C. Followingthe sintering step, the ends of the fibers are potted (static potting)with a silicon adhesive compound (Silicone AP, Dow Corning) and thepotting compound is hardened in air for 24 hours. Then the hollow fibersare cut together with the mold in such a manner that the lumina of thefibers are open. The mold with the hollow fibers is then conveyed into ahousing, with plastic seals separating the feed space from the permeatespace.

[0049] In the last example of a preferred embodiment, α-Al₂O₃ greenfibers are produced according to the Monsanto method (DE 2919560 A1).The fibers are placed in a green state in bundles on a corrugated Al₂O₃ceramic, as shown in FIG. 1. The green fibers are sintered in the moldat 1450° C. After sintering, the ends of the fibers are potted with aceramic potting compound. The potting compound has the followingcomposition:

[0050] 1180 g Al₂O₃ (CL 370 C Alcoa)

[0051] 1.76 g 4,5-dihydroxy -1,3 benzol disulfonic acid

[0052] 3.54 g uric acid

[0053] 109 g bidistilled water.

[0054] Just before casting, 2000 units of urease (EC 3.5.1.5) are added,which leads to rapid hardening of the potting compound.

[0055] After potting, the system is calcinated at 1450° C. After this,the hollow fibers are cut together with the mold in such a manner thatthe lumina of the fibers are open. A plurality of such molds containinghollow fibers is transferred into a housing with temperature stableseals, for example made of graphite, metals or HT polymers separatingthe feed space and the permeate space gas-tight. Yielded is a hollowfiber module which is suited for use at high temperatures.

[0056] If the ceramic potting compound is composed in such a manner thatthe shrinking rates of the fibers and the potting compound areapproximately the same, after placing the green fibers in the mold thefibers can be potted immediately in a green state. Fibers and pottingcompound are then sintered in the mold in a single thermal treatmentstep (cofiring process).

List of Reference Numbers

[0057] 1 mold respectively mold body

[0058] 2 grooves

[0059] 3 hollow fibers respectively capillaries

[0060] 4 recesses

[0061] 5 hole openings

[0062] 6 potting compound

[0063] 7 access openings of the mold

[0064] 8 connections for exterior inlet and outlet

[0065] 9 lumen connections

[0066] 10 housing respectively cartridge

[0067] 11 seals

[0068] 12 press plates

[0069] 13 plugs

[0070] 14 threaded rods with nuts

What is claimed is:
 1. A method for producing a hollow fibers membranemodule or a capillary membrane module, in which the hollow fibers orcapillaries (3) composed of a ceramic material or a material with aceramic-content is placed in a mold (1) structured for receiving saidhollow fibers or said capillaries (3) and is connected with said mold(1) by potting with a potting compound, wherein said hollow fibers orsaid capillaries (3) are placed in said mold (1) in an unsintered stateand sintered in said mold (1).
 2. A method according to claim 1, whereina potting compound composed of a material with a ceramic content isused.
 3. A method according to claim 2, wherein sintering said hollowfibers or said capillaries (3) and hardening said potting compoundoccurs using the same thermal process step.
 4. A method according toclaim 2 or 3, wherein the material for said potting compound and thematerial for said hollow fibers or capillaries (3) are selected in sucha manner that the thermal expansion coefficients differ by less than5*10⁻⁶ K⁻¹.
 5. A method according to claim 4, wherein said material forthe potting compound and the material for said hollow fibers orcapillaries (3) are selected in such a manner that the thermal expansionefficient of said material for said hollow fibers or said capillaries(3) is greater than or the same as the thermal expansion coefficient ofsaid material for said potting compound.
 6. A method according to one ofthe claims 2 to 5, wherein solidification of said potting compound isbrought about by altering the surface charge of the ceramic powderparticles which are a constituent of said potting compound.
 7. A methodaccording to claim 1, wherein a potting compound composed of a polymeror an organic material is used.
 8. A method according to one of theclaims 1 to 7, wherein said hollow fibers or said capillaries (3) areplaced in bundles in said mold.
 9. A method according to one of theclaims 1 to 8, wherein a mold (1) composed of porous ceramic or anotherinorganic material is used.
 10. A method according to one of the claims1 to 9, wherein a mold (1) is used which has elongated recesses forreception of said hollow fibers or capillaries (3).
 11. A methodaccording to one of the claims 1 to 10, wherein said mold (1) containingsaid hollow fibers or said capillaries (3) is attached in a housing (10)using one or a plurality of seals (11) in order to form a feed space anda permeate space which are separated from one another in a gas tightmanner by means of said seal(s) (11).
 12. A method according to claim11, wherein said mold (1) with said hollow fibers or said capillaries(3) are potted in said housing (10) with said potting compound and issubjected together with said housing (10) to a thermal process step tosinter said hollow fibers or said capillaries (3) and to harden saidpotting compound.
 13. A method according to one of the claims 1 to 12,wherein said mold (1) with said hollow fibers or said capillaries (3)and said potting compound are provided with one or a plurality ofcoatings.
 14. A device having a hollow fiber membrane module or acapillary membrane module produced according to one or a plurality ofthe preceding claims, having a housing (10) in which said mold (1) ofsaid hollow fiber membrane module or said capillary membrane modulehaving said embedded hollow fibers or capillaries (3) are disposed insuch a manner that a feed space and a permeate space are formed, withsaid housing being designed with openings (8, 9) for lumen inlet andlumen outlet as well as exterior inlet and exterior outlet and sealingbetween said feed space and said permeate space, between said lumeninlet and said lumen outlet as well as between said exterior inlet andsaid exterior outlet being produced by means of said seals (11) orsealing materials between said mold (1) and said housing (10).
 15. Adevice according to claim 14, wherein said housing (10) is designed as ametallic cartridge.
 16. A device according to claim 14 or 15, whereinsaid mold (1) is designed cylindrical in shape, is held in said housing(10) by plugs (13) inserted at the front end, and is pressed to a tightfit by said seals (11) disposed at the front end between said mold (1)and said housing (10).